The overall objective of this effort is to develop a long life, highly reliable, efficient, totally implantable compact thermal energy system to actuate cardiac assist and total heart replacement devices. The objectives of the current first phase effort are to develop, design, facricate, and test a bench model of the TRW rotary Rankine cycle engine and demonstrate 168 hours of cumulative running time with a hydraulic output of 4 watts to the blood pump using a maximum heat input of 50 watts. During the four month extension period the contractor will be directing his efforts toward the completion of the turbo pump development and the performace of component and system tests.